1. Field of the Invention
The present invention relates to a security device and, in particular, to a security device in which characteristics of a sensor circuit such as frequency and sensitivity can be set by a portable transmission unit.
2. Description of the Related Art
A theft prevention device (security device) for preventing an automobile from being stolen is designed to prevent theft in such a way that when someone opens a door of an automobile with a view to stealing it, gives a considerable shock to the automobile, or opens the trunk of the automobile while security is in force, it sounds a siren, blinks the headlights of the automobile, or cuts a starter (renders the engine incapable of being started), or cuts off fuel so that the automobile cannot run.
However, where a human body touches an automobile lightly or an automobile producing a tremendous noise passes by, a theft prevention device like a siren may by activated when no theft is intended depending on a whether the automobile is in a parking lot in which the security system is installed, or on whether it is bustling daytime or nighttime when few people are on the streets. Thus, it is considered that the frequency characteristics, sensitivity, etc. of a sensor circuit of the main body of a security system should be changable depending on the place, time, etc. in order to prevent the above-mentioned erroneous operations. However, the above-mentioned change must be made after the main body of the security system is removed, which is very annoying.